1. Field of the Invention
The present invention relates to an informationreading method using an optical card, etc.
A data recording/reproducing system which is of a type employing an optical card as a recording medium is well known in the art. This type of data recording/ reproducing system comprises: an optical card which has a plurality of parallel tracks; an optical head for optically recording data on the optical card and optically reproducing the data from the card; and a device for driving the optical card and the head relative to each other such that the optical head moves in both the longitudinal and widthwise directions of tracks.
An example of a known optical card is disclosed in Published Unexamined Japanese Patent Application (PUJPA) No. 63-37876. As is shown in FIG. 1, the known optical card 1 has a plurality of tracks 2 extending in parallel to one another in the longitudinal direction of the card 1. Each track 2 is comprised of: ID sections 3a and 3b which are located at the respective longitudinal ends and are used for storing track address information; and a data section 4 which is located between the ID sections 3a and 3b and is used for storing data. FIG. 2 shows one of the tracks 2 in an enlarged scale. As is shown in FIG. 2, the left-side ID section 3a is made up of: a pull-in area 5a of a data-separation PLL; an area 6a in which a synchronous signal indicating the start of track address information is recorded; and an area 7a in which the track address information is recorded. Likewise, the right-side ID section 3b is made up of: a pull-in area 5b of a data-separation PLL; an area 6b in which a synchronous signal indicating the start of track address information is recorded; and an area 7b in which the track address information is recorded. It should be noted that areas 5a, 6a and 7a of the left-side ID section 3a and areas 5b, 6b and 7b of the right-side ID section 3b are symmetrical with each other.
A description will be given as to how data is written or read out of the data section 4.
The optical card 1 is irradiated with a convergent light beam, with the light beam reflected by the optical card 1 being received by the optical head. In this state, the optical card 1 and the optical head are driven relative to each other such that the optical head moves in the lateral direction of the tracks of the card 1, so as to confirm the position of the current track. The position of the current track and the position of a target track are compared with each other, for the measurement of the distance therebetween. The optical head is moved for the measured distance in the widthwise direction of tracks, to thereby seek the target track. When the optical head has reached the target track, it writes data on the data section 4 of the target track or reads it out of that data section 4. In the case where the optical head moves from the left-side portion of the card 1 to the right-side portion thereof (which direction will be hereinafter referred to as a "forward direction"), the optical head reads information from the right-side ID section 3b, to thereby confirm that the optical head is at the target track. Conversely, in the case where the optical head moves from the right-side portion of the card 1 to the left-side portion thereof (which direction will be hereinafter referred to as a "backward direction"), the optical head reads information from the left-side ID section 3a, to thereby confirm that the optical head is at the target track.
Usually, the optical card 1 is carried with the user. It is therefore likely that dust particles will adhere to the recording surface of the optical card 1. It is also likely that the recording surface of the optical head 1 will be scratched. If the recording surface of the optical card 1 has dust particles or scratches thereon, the optical head cannot accurately move to the target track, resulting in a tracking error.
When data is written in the data section 4 of a given track 2 or read out of the data section 4, the information stored in either ID section 3a or 3b is read, as mentioned above In the prior art, however, this information is read merely for confirming whether or not the radial beam spot is located at the given track 2. This being so, the track address information is read only once; it is read immediately before data is written or read. However, this prior art technique does not always ensure satisfactory data reading if the card 1 has dust particles or scratches on the recording surfaces. Assume that the optical head is shifted from the target track to an adjacent track during data writing, due to dust particles or scratches. Since such a shifting movement of the optical head cannot be detected in the prior art technique, data is undesirably written on the data section 4 of the adjacent track, not that of the target track.